Terms of Services and Privacy Policies depend on the legal entity behind a website. They shouldn't be done based on how domain or subdomain are structured.
These legal agreements are binding between the company that operates the website/mobile app and users.
What you should look after is:
Making sure that both legal agreements are based on what personal information you collect, use and store from all subdomains and websites.
That you link to both legal agreements from all subdomains and websites since they share the same agreements.